Radiation detector, radiation detector element, and radiation imaging apparatus

ABSTRACT

In a gamma camera, a plurality of radiation detector elements having a rod-shaped first electrode, a semiconductor device surrounds the first electrode to contact with it for entering a radiation, and a second electrode provided for the side surface of the semiconductor device are detachably attached to a holding member. The holding member has a first electrode contact portion contacted with the first electrode and a second electrode contact portion contacted with the second electrode. A collimator in which a plurality of radiation paths provided corresponding to the plurality of radiation detector elements are formed is arranged on the radiation entering side of the plurality of radiation detector elements. A γ-ray detection signal outputted from the first electrode contact portion is sent to a signal processing integrated circuit. A high voltage is applied to the second electrode via the second electrode contact portion.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to detection and an imaging operation of aradiation such as X-ray, γ-ray, or the like and, more particularly, to aradiation detector, a radiation detector element, and a radiationimaging apparatus for detecting a γ-ray of high energy.

2. Description of the Related Art

When taking a medical X-ray as an example, as well as a radiationimaging apparatus of a film type, radiation imaging apparatuses such asimaging plate and flat panel detector (FPD) having both excellentresolving power and resolution have been developed. As a detectorelement, there has been used: a scintillation detector formed bycombining a scintillator which reacts on a radiation and emits light anda photomultiplier or a photodiode which converts the light into charges;or a solid state device such as a semiconductor radiation detector whichreacts on the radiation and directly collects generated charges or thelike. For example, the FPD using a number of scintillation detectors isa large-area imaging apparatus which can image a transmission X-ray in amanner similar to a conventional X-ray imaging film. An X-ray signaldetected in the detector element is read out from a detector elementsubstrate of a large area comprising one or a plurality of sheets byusing a TFT technique or the like. As a name “flat panel” shows that thedetector element is very thin and the detector itself has a plate shape.

According to a gamma camera (radiation detector) for imaging a γ-rayemitted from a chemical-ray source dosed into a human body, since energyof the γ-ray which is used is higher than that of the X-ray, if theγ-ray is used as it is, sensitivity of the gamma camera deterioratesremarkably. That is, with a thickness of the detector element which isused in an X-ray imaging apparatus, a reaction probability of the γ-rayis low and the γ-ray passes through the detector element as it is.Therefore, to improve the sensitivity by raising the reactionprobability in the detector element, the detector element needs to havea thickness of a certain extent in the incident direction of the γ-ray.That is, the detector element itself has directivity. Accordingly,unless the incident direction of the γ-ray is specified for such adetector having the directivity, space resolution cannot be obtained.

Generally, to specify the incident directivity of the γ-ray, a slitcalled a collimator or a thick porous metal plate is arranged in frontof the detector. (Refer to “Medical Image• Radiation ApparatusHandbook”, Japan Industries Association of Radiological Systems, page184)

FIG. 25 shows a construction of a conventional gamma camera disclosed inthe above reference. At present, a gamma camera using an NaIscintillator is still a mainstream. The gamma camera of FIG. 25 alsouses a similar scintillator 31. A radiation enters the scintillator 31at an angle limited by a collimator 41 e and scintillation light isemitted. The light reaches a photomultiplier 33 through a light guide 32and becomes an electric signal. The electric signal is shaped by ameasuring circuit 34 attached to a measuring circuit fixing board 35 andsent from an output connector 46 e to an external data collectingsystem. A whole camera is enclosed in a light shielding casing 47 e,thereby shielding external electromagnetic waves other than theradiation.

Generally, since the gamma camera using the scintillator 31 as shown inFIG. 25 has a structure in which the large photomultiplier 33 isarranged behind a crystal of large scintillator 31 of one sheet, itsspace resolution is no more than equal to about 10 mm. When thescintillator 31 is utilized, it detects the radiation via multi-levelconversion from the radiation to the visible light and from the visiblelight to electrons, there is a problem such that energy resolution islow. Therefore, at present, a radiation detecting apparatus having asemiconductor radiation detector element for directly converting theradiation into the electric signal in place of the scintillator 31 hasbeen developed. (“Radiation Detection and Measurement, the 3rd edition”,The Nikkan Kogyo Shimbun Ltd., page 903).

In a conventional gamma camera (semiconductor radiation detector) shownin FIG. 26A, a semiconductor device 77 has electrodes (an anode 78 and acathode 79). The semiconductor device 77 has a construction in which theanodes 78 are arranged in a lattice form by the electrodes 78 and 79(“Radiation Detection and Measurement, the 3rd edition”, The NikkanKogyo Shimbun Ltd., page 903). Reference numeral 41 e denotes thecollimator; 44′ a board for installing semiconductor device and an ASIC;45 c an ASIC (Application Specific Integrated Circuit) as an IC for areading circuit; 46 c an output connector to output a detection signal;and 47 c a light shielding casing to shield the visible light andelectromagnetic waves.

Also in the gamma camera, as same as in the FPD, realization of a largeimaging area is indispensable. A number of detector elements arenecessary in association with the realization of the large area. In thecase of the scintillation detector, such a number of detector elementsare separated as elements by the photomultiplier or photodiode disposedadjacently to one large device substrate. In the case of thesemiconductor radiation detector, they are separated as elements bypattern wirings of the electrodes 78 and 79 as shown in FIG. 26B. Toremove scattered components of the γ-ray, intensity information of theγ-ray is obtained by counting pulses. For this purpose, a preamplifier,a waveform shaping circuit, a peak detecting circuit, and the like arenecessary for each element and an extremely large number of circuits arenecessary in the case of a large area. Therefore, by using the ASIC 45 cfor those circuits, saving of space is realized.

In the conventional semiconductor radiation detector as shown in FIGS.26A and 26B, however, even if the collimator 41 e is used, the γ-rayscattered in the detector element 77 (scintillator 31) enters theadjacent cell and exercises an influence thereon. This kind ofscattering radiation detection (refer to γ₁′ in FIG. 14) and causes adeterioration in space resolution. To avoid an inconvenience caused bysuch a phenomenon, in the radiation detector, an incident position isidentified by energy of the incident γ-ray (γ₀) That is, since areaction signal (ΔE₀₀) near the energy of the γ-ray emitted from a γ-raysource 16 d is discriminated and selectively detected, sensitivitydeteriorates more. That is, the sensitivity of the radiation detector isextremely lowered by the inherent low sensitivity, the decrease inincident γ-ray due to the collimator 41 e, and the discrimination of theenergy. Although a hole diameter of the collimator 41 e is increased andan incident dose is increased while sacrificing the space resolution inorder to compensate the deterioration in sensitivity, the higher theenergy of the γ-ray to be detected is, the thicker a wall of thecollimator 41 e has to be. Consequently, not only the space resolutiondeteriorates even more but a weight increases and maintenance efficiencyof the radiation detector or the radiation imaging apparatus alsodeteriorates.

Since a number of radiation detector elements (pixels) are necessary forthe large-area imaging, use of the ASIC and the element separation byelectrode patterning of a signal lead-out portion are indispensable.However, they cause the following problems.

-   (1) An installing board of the detector and the ASIC are    integratedly formed by bumping or the like and if one pixel is    destroyed, the board has to be exchanged on a large unit basis.    Since the detector element is very expensive, the exchange of the    board on a large unit basis denotes that large costs are required.-   (2) Also in view of the manufacturing of the camera, since the    detector elements and the ASIC are installed onto one installing    board, assembling steps of the camera are extremely complicated and,    even if a defective element is found, it cannot be exchanged.-   (3) Particularly in the radiation detector for imaging the    high-energy γ-ray, a length of collimator is long, a total length of    radiation imaging apparatus is very long, and it is very heavy and    large in size. This causes an enlargement in size of the apparatus    in terms of intensity of structure members which support a camera    unit and results in an increase in costs, a deterioration in    maintenance efficiency, and an increase in anxiety of the patient.

In other words, it causes a deterioration in maintenance efficiency ofthe radiation detector and the radiation imaging apparatus.

SUMMARY OF THE INVENTION

It is, therefore, an object of the invention to improve sensitivity(effective count, S/N ratio and maintainability) of a radiation of aradiation detector and a radiation imaging apparatus.

To accomplish the above object, a radiation detector according to theinvention comprises a plurality of radiation detector elements eachhaving: a rod-shaped first electrode; a semiconductor device whichsurrounds an ambience of the first electrode and is come into contactwith the first electrode and into which a radiation enters; and a secondelectrode provided for the side surface of the semiconductor device.Thus, sensitivity to the radiation (effective count, S/N ratio) can beraised. The radiation detector includes a gamma camera.

More preferably, the radiation detector comprises an element holdingmember (for example, detector module board) having: a plurality ofholding units for detachably holding the radiation detector elements;and an electric connecting portion for electrically connecting anodesand cathodes of the radiation detector elements. An integrated circuitholding member (for example, ASIC module board) in which the elementholding member and the integrated circuit (ASIC) have been installed isconnected so that it can be separated. The semiconductor radiationdetector element is set into a coaxial shape (shape in which asemiconductor device is arranged around (outer periphery) of arod-shaped anode and a cathode is arranged around (outer periphery) ofthe semiconductor device) or a laminate structure. A shield of theradiation is arranged between the radiation detector elements. Thus,together with maintainability, the space resolution to the radiation canbe raised.

Other objects, features and advantages of the invention will becomeapparent from the following description of the embodiments of theinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic external view of a gamma camera apparatus as aradiation imaging apparatus of an embodiment according to the invention;

FIG. 2 is a schematic vertical sectional view of the gamma camera in thefirst embodiment according to the invention;

FIG. 3 is a partially enlarged diagram of FIG. 2;

FIG. 4 is a schematic vertical sectional view of a gamma camera ofanother embodiment to which a converging collimator is applied;

FIG. 5 is a schematic vertical sectional view of another embodiment of agamma camera;

FIG. 6 is a schematic vertical sectional view of a gamma camera of thesecond embodiment according to the invention;

FIG. 7 is a perspective view of a shield in FIG. 6;

FIG. 8 is a perspective view of another embodiment (a short shield) ofthe shield;

FIG. 9 is a perspective view of another embodiment (a plurality ofshields) of the shield;

FIG. 10 is a perspective view of a shield to which a detector elementshown in FIG. 22B is applied;

FIG. 11A is an explanatory diagram showing a holding state of a detectorelement shown in FIG. 6 in the shield;

FIG. 11B is an explanatory diagram showing a holding state of thedetector element shown in FIG. 22 in the shield;

FIG. 12 is an explanatory diagram showing a principle for preventing ascattering radiation from adjacent pixels in the gamma camera shown inFIG. 6 by the shield;

FIG. 13 is an explanatory diagram showing a scattering radiation fromadjacent pixels removing effect in the gamma camera shown in FIG. 6;

FIG. 14 is an explanatory diagram showing a generation principle of ascattering within detector in a conventional gamma camera shown in FIGS.26A and 26B;

FIG. 15 is an explanatory diagram showing energy spectrum of detected γray obtained in the detector;

FIGS. 16A to 16C are diagrams showing an example of distribution ofmeasured radiation from γ-ray sources of different energy levels;

FIG. 16A is an explanatory diagram showing a spacial relation betweentwo γ-ray sources and the detector;

FIG. 16B is an explanatory diagram showing the example of the measuredradiation distribution in the γ-ray of 140 keV in FIG. 16A;

FIG. 16C is an explanatory diagram showing the example of the measuredradiation distribution in the γ-ray of 511 keV in FIG. 16A;

FIG. 17 is a schematic vertical sectional view of another embodiment(using a scintillator) of a gamma camera;

FIG. 18A is a perspective view of a detector element which is used in agamma camera in the third embodiment according to the invention;

FIG. 18B is a perspective view showing a state where a plurality ofdetector elements of FIG. 18A are arranged;

FIG. 19A is a perspective view of a semiconductor device member which isused in another embodiment of a detector element;

FIG. 19B is a perspective view of another embodiment of a detectorelement constructed by the semiconductor device members of FIG. 19A;

FIG. 20A is a perspective view of a semiconductor device member which isused in a detector element of FIG. 20C;

FIG. 20B is a perspective view of an anode which is used in the detectorelement of FIG. 20C;

FIG. 20C is a perspective view of another embodiment of the detectorelement;

FIG. 21A is a perspective view of a semiconductor device member which isused in a detector element of FIG. 21C;

FIG. 21B is a perspective view of an anode which is used in the detectorelement of FIG. 21C;

FIG. 21C is a perspective view of another embodiment of the detectorelement;

FIG. 22A is a perspective view of a semiconductor device member which isused in the detector element of FIG. 22B;

FIG. 22B is a perspective view of another embodiment of the detectorelement;

FIG. 23 is a constructional diagram of a radiation imaging apparatus(SPECT apparatus);

FIG. 24 is a constructional diagram of a radiation imaging apparatus(PET apparatus);

FIG. 25 is a constructional diagram showing a conventional example of agamma camera;

FIG. 26A is a constructional diagram showing another conventionalexample of the gamma camera;

FIG. 26B is a perspective view of a detector element shown in FIG. 26A;and

FIG. 27 is a cross sectional view of a collimator which is used in theconventional gamma camera.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Embodiments (first to third embodiments) of the invention will bedescribed in detail hereinbelow with reference to the drawings. Thefirst embodiment relates to a radiation detector, an attaching structureof parts and the like in a radiation imaging apparatus, and a connectingstructure. The second embodiment relates to miniaturization andsimplification of a collimator in the radiation detector. The thirdembodiment relates to a structure of a detector element (radiationdetector element) in the radiation detector.

<<First Embodiment>>

A gamma camera imaging apparatus of the first embodiment to improvemaintenance performance or the like of a radiation detector by theattaching structure and the connecting structure will be described withreference to FIG. 1 and the like. FIG. 1 is a schematic side sectionalview of a gamma camera.

[Gamma Camera Imaging Apparatus (Radiation Imaging Apparatus)]

A gamma camera imaging apparatus is a kind of nuclear medicinediagnosing apparatus. According to this apparatus, a radiomedicine dosedinto a human body is accumulated or deposited in the body, a γ-rayemitted from the radiomedicine is measured from a position out of thebody, and a diagnosis is assisted on the basis of an accumulation degreeor the like. For example, ¹³¹I is dosed into the human body in a form ofsodium iodide and an accumulation degree of sodium iodide accumulated ina thyroid gland is measured from a position out of the body, therebyexamining a function of the thyroid gland.

In the gamma camera imaging apparatus of FIG. 1, a subject 17 a dosedwith a medicine containing RI (Radioisotope) nuclear species asmentioned above is put on a bed 12 a and a γ-ray 18 a which is radiatedfrom a chemical-ray source 16 a accumulated in a diseased part or thelike of the subject 17 a is imaged by a gamma camera (radiationdetector) 10 a attached to a gamma camera casing 11 and disposed abovethe subject 17 a. A data processing apparatus 13 a for imaging signalinformation obtained from the gamma camera 10 a, a monitor 15 a fordisplaying the image, and an input device (keyboard) 14 a are arrangedbeside the casing 11. It is not always necessary that those dataprocessing systems are located near the casing 11. The gamma cameraimaging apparatus is constructed as mentioned above.

[Gamma Camera]

Subsequently, a construction of the gamma camera 10 a equipped for thegamma camera imaging apparatus will be described with reference to FIG.2 and the like. When a first electrode is an anode, a second electrodeis a cathode. When the first electrode is the cathode, the secondelectrode is the anode. In the following embodiments, the anodecorresponds to the first electrode and the cathode corresponds to thesecond electrode.

The gamma camera 10 a shown in FIG. 2 is constructed so as to include: acollimator 41 a; a plurality of radiation detector elements(hereinafter, simply referred to as detector elements) 71 a fordetecting the γ-ray; and an ASIC (Application Specific IntegratedCircuit) 45 a for processing γ-ray detection signals (radiationdetection signals) outputted from the detector elements 71 a. Thedetector elements 71 a are detachably held and fixed to a detectormodule board (element holding member) 42 a every element. An ASIC moduleboard (integrated circuit holding member) 43 a on which the ASIC 45 ahas been set is arranged behind the detector module board 42 a andconnected to the detector module board 42 a by a connector (anode signalline connectors 48 a and 49 a; cathode potential supplying connectors 48b and 49 b) and they are also detachable. The ASIC 45 a is connected toan output connector 46 a attached to a rear surface of the gamma camera10 a. Obtained data is sent from the output connector 46 a to a datacollecting apparatus (not shown). Although a signal is transmitted andreceived by the anode and an electric potential is supplied by thecathode in the embodiment, on the contrary, it is also possible tosupply the electric potential by the anode and transmit and receive thesignal by the cathode.

Parts including the detector elements 71 a and the ASIC 45 a are coveredby a light shielding casing 47 a in order to avoid an influence ofnoises due to the light and an influence of electromagnetic noises. Theconstruction described so far relates to a main body of the gamma camera10 a. The collimator 41 a to specify the direction of the incident γ-rayis disposed in front of the gamma camera 10 a. The collimator 41 a ismade of a metal which largely attenuates the γ-ray, for example, aradiation shielding material such as lead or tungsten and a plurality ofelongated holes (radiation paths) 19 for passing the γ-ray are formed inthe collimator. The collimator 41 a is detachable from the main body ofthe gamma camera 10 a in order to change the kind of collimator andexchange and use it in accordance with energy of the incident γ-ray. Thegamma camera 10 a is obtained by covering the whole assembly includingthe collimator 41 a by the casing.

A connection of the detector module board 42 a and the ASIC module board43 a will be described hereinbelow with reference to FIG. 3.

As shown in FIG. 3, the detector element 71 a (coaxial electrodeelement) is constructed so as to include: a rectangular parallelepipedsemiconductor device 74; a cathode 73 a formed thinly by a conductivematerial onto an outer periphery (the whole side surface) of thesemiconductor device 74; and an anode (anode pin) 72 a pierced at thecenter of the semiconductor device 74. The anode 72 a is pierced so asto be projected from a rear edge portion of the detector element 71 a.An explanation will be made on the assumption that the incident side ofthe γ-ray of the detector element 71 a is set to a front edge portionand its opposite side is set to the rear edge portion. The detectorelement 71 a corresponds to a radiation detector element in which asemiconductor material which reacts on the radiation and generatescharges is arranged around (outer periphery) the first electrode (anode72 a) formed in a rod shape and the second electrode (cathode 73 a)whose polarity differs from that of the first electrode (anode 72 a) isarranged around (outer periphery) the semiconductor material in a layershape (film shape). Specially, the detector element 71 a corresponds toa coaxial element having a construction in which the semiconductormaterial or the like is coaxially arranged.

A plurality of holding portions H as hole portions each for enclosingand holding the rear edge portion of a predetermined length of thedetector element 71 a are provided for the detector module board 42 ashown in FIG. 3. The holding portion H has a large diameter portion anda small diameter portion. A rear edge portion of the semiconductordevice 74 is inserted into the large diameter portion. The anode (anodepin) 72 a projecting from the rear edge portion of the detector element71 a is inserted into the small diameter portion. A pair of cathodespring electrodes 55 a which are come into contact with the rear edgeportion of the detector element 71 a are provided in the large diameterportion in each holding portion H so as to face each other. The cathodespring electrodes 55 a have functions for holding the detector element71 a and supplying the cathode potential. A pair of anode springelectrodes 55 b are provided in the small diameter portion in eachholding portion H so as to face each other. The anode spring electrodes55 b hold (attach) the detector element 71 a so as to be detachable fromthe detector module board 42 a. Since a leaf spring is bent in an arcshape as each of the cathode spring electrodes 55 a and the anode springelectrodes 55 b, the detector element 71 a is certainly held and alsoeasily detachable.

In the embodiment, the cathode spring electrodes 55 a and the anodespring electrodes 55 b can be also provided on the detector element 71 aside. In this connection, the detector module board 42 a corresponds toa construction such that a plurality of holding portions H to detachablyhold the detector element 71 a for detecting the radiation via both ofthe spring electrodes 55 a and 55 b are arranged in front of thedetector element 71 a and a plurality of electric connecting portions(holding portions H) to electrically connecting the anode 72 a and thecathode 73 a of the detector element 71 a held in the holding portion Hare arranged. The gamma camera 10 a in the embodiment corresponds to a“radiation detector” of Claims.

As shown in FIG. 3, the connectors 48 a and 48 b are provided for thedetector module board 42 a and the connectors 49 a and 49 b are providedfor the ASIC module board 43 a, respectively. The connectors 48 a and 49a are fitted into each other. The connectors 48 b and 49 b are fittedinto each other. In FIG. 3, to clearly show the construction of theconnectors 48 a, 48 b, 49 a, and 49 b, the connectors 48 a and 49 a andthe connectors 48 b and 49 b are separately shown, respectively.However, actually, the connector 48 a is fitted into the connector 49 aand the connector 48 b is fitted into the connector 49 b, respectively.Owing to the fitting of those connectors, the detector module board 42 ais attached to the ASIC module board 43 a.

The connector 48 a has signal transfer pins 48 ap electrically connectedto the anode spring electrodes 55 b (in a one-to-one correspondencerelation manner) each of which is come into contact with the anode 72 aof each detector element 71 a. Each signal transfer pin 48 ap isinserted into each of the same number of receiving portions 49 ahprovided for the connector 49 a. The connector 48 b connected to thecathode spring electrodes 55 a provided for each holding portion H has apotential supplying pin 48 bp. The potential supplying pin 48 bp isinserted into a receiving portion 49 bh which is formed in the connector49 b. Owing to such a structure, the detector module board 42 a and theASIC module board 43 a are certainly connected. The detector moduleboard 42 a and the ASIC module board 43 a can be also removed bydisconnecting them.

Subsequently, the operation of the gamma camera 10 a will be described.

As shown in FIGS. 2 and 3, it is assumed that the γ-ray entered from theleft side of the diagram. Since the γ-ray which reached the collimator41 a is attenuated by the material constructing the collimator 41 a inportion other than the elongated hole 19, it cannot reach the detectorelements 71 a. Therefore, the incident direction of the γ-ray whichpassed through the elongated hole 19, reached the detector elements 71a, and was detected by the detector elements 71 a is specified.Therefore, the position where the γ-ray was emitted can be specified.The detector elements 71 a collects the electrons and holes formed inthe semiconductor device 74 by the incidence of the γ-ray onto the twoelectrodes of the anode 72 a and the cathode 73 a, thereby detecting theincidence of the γ-ray. Energy of the incident γ-ray can be alsospecified from an amount of charges corresponding to an amount of thecollected electrons and holes. A γ-ray detection signal having such acharge amount is outputted from the anode 72 a of the detector element71 a and transferred to the ASIC 45 a via the anode spring electrodes 55b, signal transfer pins 48 ap, and receiving portion 49 ah. The ASIC 45a processes the γ-ray detection signal generated from each detectorelement 71 a and outputs obtained information to the data processingapparatus 13 a for imaging it. A high voltage which is generated from ahigh voltage power source (not shown) is transferred to each cathodespring electrode 55 a via the receiving portion 49 bh and the potentialsupplying pin 48 bp and applied to the cathode 73 a of each detectorelement 71 a. The detecting operation of the signal in the detectorelement 71 a will be described in detail in an embodiment of an element,which will be explained hereinlater.

A conventional example will be described hereinbelow with reference toFIGS. 26A and 26B for the purpose of comparing.

In the conventional gamma camera shown in FIG. 26A, the detector element77 is a single large substrate and is constructed as a pixel by apattern of the electrode 78 as shown in FIG. 26B. The detector element77 is completely fixed by solder bumping or the like onto the substrate44′ on which the ASIC 45 c has been installed (other portions aresimilar to those described with reference to FIG. 2 and the like).

Since such a construction is used, in the conventional gamma camera, ifone imaging pixel is destroyed, the whole substrate 44′, in turn, thewhole ASIC 45, that is, the whole gamma camera has to be exchanged, sothat very expensive maintenance costs are required. Even if a defectiveelement (defective pixel) is found out after connecting to the ASIC 45,it cannot be exchanged. Particularly, in the semiconductor radiationdetector, the reliability for all detector elements 77 is insufficientyet and it becomes a large obstacle when the imaging apparatus of alarge area is put into practical use.

In the embodiment, the structure such that the detector elements areindividually detachable is used in consideration of such maintenanceperformance. Even if one detector element is destroyed, it can beexchanged on a detector element unit basis.

For example, in a condition such that separating type elements (elementsof a 3 mm-square) of 1000 ch (1000 channels) are arranged onto a moduleboard of a 10 cm-square, hitherto, if tens of elements (pixels) arebroken, the camera module (substrate 44′) is exchanged. On the otherhand, in the embodiment, since the detector elements 71 a can beexchanged one by one, the costs can be reduced into about 1/30. In theconventional technique, even if the element is slightly damaged, it iscontinuously used in consideration of a relation between atroublesomeness and the costs, so that a clear image cannot be obtainedin many cases. On the other hand, according to the gamma camera 10 a ofthe embodiment, a clear image can be obtained by making simplemaintenance.

Unlike the prior art, the embodiment has a construction such that thedetector module board 42 a and the ASIC module board 43 a can beseparated. By constructing as mentioned above, the ASIC 45 a with thehigh reliability and the detector elements 71 a whose reliability cannotbe assured can be separated after the destruction, so that degrees offreedom regarding the manufacturing and the maintenance can be raised.Although the bumping connection has been used hitherto for connection ofthe detector elements 77 and the substrate 44′, in the embodiment, sincethe bumping connection is unnecessary, an influence of heat which iscaused upon bumping connection can be avoided.

Further, in the embodiment, even if the subject is imaged by using thesame ASIC 45 a, the detector elements can be changed to the detectorelements 71 a in accordance with an energy level of the γ-ray which isused for imaging. For example, in the semiconductor radiation detector,although a CdTe (cadmium telluride) element or an element called CZT hashigh detecting performance, in the case of imaging mainly by low energy,it is sufficient to buy a gamma camera using a GaAs (gallium arsenide)element that is cheaper than CdTe, buy a CdTe element module (detectormodule board 42 a) which can also cope with the imaging using highenergy as necessary, and exchange only the module board 42 a. In otherwords, it is sufficient to separately prepare and exchange only thedetector module board 42 a to which the detector elements 71 a have beenattached or only the detector elements 71 a. Therefore, there is no needto newly buy another gamma camera 10 a. In a low-energy region of amedical X-ray level, further cheap Si elements can be also used asdetector elements 71 a.

By connecting not only the parallel collimator 41 a as shown in FIGS. 2and 3 but also a converging collimator 41 d (refer to a gamma camera 10b shown in FIG. 4) for enlargedly imaging a small portion, the detectormodule board 42 a having an element arrangement corresponding to adiverging collimator for reduction imaging a range larger than an areaof a camera, or the like, the detector elements 71 a (detector moduleboard 42 a) or the collimators 41 a and 41 d according to the userobject can be also selected in one ASIC module board 43 a. It isdifficult to perform such an imaging by the detector elements on onesubstrate on which a partition corresponding to each pixel is notprovided in the detector element. That is, it is because in thedetection of the high-energy γ-ray, the element needs a thickness(depth) and a detection volume has directivity. In the embodiment, sincethe substrate is partitioned every pixel and axial directions of thedetector elements 71 a are aligned in the incident direction of theγ-ray of the imaging region, it is also possible to image by thehigh-energy γ-ray.

Since a variation in imaging form is increased as mentioned above, inaddition to a conventional simple equal magnification plane image, animaging application of the gamma camera 10 can be enlarged.

As mentioned above, according to the first embodiment, advantages suchas improvement of the maintenance performance, reduction of themaintenance costs, assurance of the reliability in terms of themanufacturing and maintenance, enlargement of the application range, andthe like are obtained.

Although the construction in which the detector module board 42 a andthe ASIC module board 43 a can be separated has been shown in FIG. 2 andthe like, both of them can be also integrated so that they cannot beseparated as shown at 44 in a schematic vertical sectional view of agamma camera 10 c in FIG. 5. In the construction of FIG. 5, the detectorelements 71 a can be separated one by one.

An arrangement of the holding portions H to hold the detector elements71 a on the detector module board 42 a can be set to, for example, alattice shape such as checkers. For example, if the detector element 71a has a hexagonal cross section, the arrangement of the holding portionsH can be set to a honeycomb-shape.

<<Second Embodiment>>

Subsequently, a gamma camera imaging apparatus of the second embodimentto improve the weight saving, downsizing and sensitivity or the like bysaving (miniaturization) of collimators will be described with referenceto FIG. 6 and the like.

It is a large feature of a gamma camera 10 d of the second embodimentshown in FIG. 6 that the collimator 41 a (refer to FIG. 2 and the like)as shown in the first embodiment is omitted (made to be unnecessary).The gamma camera 10 d has a lattice-shaped shield 50 b constructing aplurality of holding portions H1 as through-holes. Each detector element71 a is fitted and held into each holding portion H1. That is, a wholeperiphery (excluding a front edge surface and a rear edge surface) ofthe detector element 71 a is surrounded by the shield 50 b. The shield50 b is made of a conductive radiation shielding material.

In association with the construction such that the detector element 71 ais held by the shield 50 b as mentioned above, a cathode potential issupplied to each detector element 71 a via the conductive shield 50 b. Adetector module board 42 b has a plurality of holding portions H1 eachof which is constructed in a manner such that the cathode springelectrode 55 a and the large diameter portion of the holding portions Hare removed from the foregoing detector module board 42 a and a smalldiameter portion provided with the anode spring electrode 55 b isformed. The number of holding portions H1 is the same as the number ofdetector elements 71 a. The anode 72 a is come into contact with theanode spring electrode 55 b. The potential supplying pin 48 bp isconnected to the shield 50 b. Since other component elements, that is,the ASIC module board 43 a, the connectors 48 a, 48 b, 49 a, and 49 b,the ASIC 45 a, and the output connector 46 a are similar to those in thefirst embodiment described with reference to FIG. 2 and the like, theirexplanation is omitted here. That is, the gamma camera 10 d of thesecond embodiment also corresponds to a construction such that theshield 50 b to shield the γ-ray is arranged between the detectorelements 71 a of the radiation detector (gamma camera 10 d) having aplurality of detector elements 71 a for detecting the radiation, or thelike.

The portions of the shield 50 b and the detector elements 71 a extractedfrom FIG. 6 are shown in a perspective view of FIG. 7. As shown in FIG.7, the detector element 71 a is arranged in each holding portion H1 ofthe lattice-shaped shield 50 b. Each detector element 71 a is eitherdetachable as mentioned in the first embodiment or undetachable (in thefollowing explanation, it is presumed that the detector element 71 a isdetachable).

FIG. 11A shows an example of a holding structure for holding thedetector elements 71 a. In the shield 50 b, the cathode spring electrode55 a which is bent in an arc-shape is arranged on the inside of eachholding portion H1. The detector element 71 a is detachably fixed by thecathode spring electrode 55 a. The detector element 71 a is a coaxialelectrode element similar to that in the first embodiment and has twoelectrodes of a center axis and the whole side surface. The outer (thewhole side surface) electrode between them is the cathode 73 a. Bysupplying a cathode potential to the shield 50 b by the potentialsupplying pin 48 bp, the same electric potential is applied to all ofthe detector elements 71 a which are in contact with each cathode springelectrode 55 a. The detector element 71 a having the coaxial anode 72 ais used and its effects and the like will be described hereinlater.

In the above construction, the shield 50 b effectively uses a gapbetween the detector elements 71 a existing in the first embodiment. Afront edge portion of the shield 50 b plays a role of the collimator 41a in the first embodiment. The shield 50 b can be made of the samematerial as that of the collimator 41 a in the first embodiment. Thedetector element 71 a can be detached by inserting a dedicated pair oftweezers into a gap between the detector element 71 a and the shield 50b.

The detecting operation and advantages in the second embodiment will bedescribed with reference to FIGS. 12 and 13 in comparison with a priorart of FIGS. 14 and 15.

FIG. 14 shows a main signal component which is detected in the detectorelement 77 (scintillator 31). FIG. 15 shows an energy spectrum of adetection signal which is obtained in one detector element (pixel). Thecollimator 41 e shown in FIG. 14 is shown as if its length wereconsiderably short for convenience of illustration. Actually, it is verylong as shown in FIG. 27. In FIG. 14, reference numeral 16 d denotes aγ-ray source (RI nuclear species in the human body of a subject); 17 d asubject; 18 d a γ-ray emitted from the γ-ray source 16 d; and 77 thedetector element. FIGS. 12 and 13 show similar information which isobtained in the second embodiment.

First, the detecting operation of the prior art will be described withreference to FIG. 14 and the like.

The γ-ray shown at 18 d is emitted from the γ-ray source 16 d in thesubject 17 d. At this time, it is assumed that only the γ-ray of γ₀(energy E₀) is emitted from the γ-ray source 16 d. Although the γ-ray isisotropically emitted from the γ-ray source 16 d, only the γ-ray whichpasses through the collimator 41 e is shown in FIG. 14. To the γ-ray γ₀(direct γ-ray) which passed through the collimator 41 e, totalabsorption (ΔE₀₀) of the energy due to a photoelectric effect and adecrease in the energy (energy of ΔE₀₁ is emitted) due to scatteringoccur in the detector element 77 (scintillator 31). Energy E₁ of ascattered γ-ray γ₁ is smaller than the energy E₀ of the original γ-rayγ₀ (E₁<E₀). Assuming that the scattered γ-ray γ₁ is total-absorbed bythe photoelectric effect in the same pixel, energy ΔE₁₁ is emitted. Atotal value of ΔE₁₁ and ΔE₀₁ is equal to ΔE₀₀. Each of the γ-ray γ₀ andγ-ray γ₁ is the γ-ray whose incident direction is specified by thecollimator 41 e. As mentioned above, by obtaining the signal of thetotal absorption (ΔE₀₀) of the energy due to the photoelectric effect,the more correct position image information of the γ-ray source 16 d canbe obtained.

However, as already described above, the scattered γ-ray γ₁ in thedetector element 77 (scintillator 31) is not always absorbed in the samepixel as that in which the scattering occurred. There is a phenomenoncalled a scattering radiation detection such that the γ-ray is scatteredinto the adjacent pixel (portion to detect the γ-ray γ₀ which inherentlyenters from a neighboring gap of the collimator 41 e) and absorbedthere. Energy absorbed due to the scattering radiation detection fromadjacent pixels is assumed to be ΔE₁₁′. Besides, the γ-ray scattered inthe human body of the subject 17 d enters. That is, although the γ-rayγ₀ of one kind of energy is radiated from the γ-ray source 16 d, γ-rayphotons which are actually detected by the detector element 77 (or thephotomultiplier 33 (refer to FIG. 25) provided on the post stage side ofthe detector element 77 (scintillator 31) are recognized as γ-rayshaving different energy as mentioned above.

FIG. 15 shows energy spectra of detected count values of the γ-rayshaving different energy with respect to a certain pixel.

A scattering radiation in the detector (γ₁′) is detected irrespective ofthe position of the γ-ray source 16 d, gives false position information,and causes spacial resolution of the image to deteriorate. A signalshowing true position information of the γ-ray source 16 d is only thetotal-absorbed signal component of ΔE₀₀, as shown as hatched part in thefigure. Therefore, usually, it is necessary to make energydiscrimination every detection signal and improve quality of the imageby using only the signal of ΔE₀₀ as a signal of a certain energythreshold value Et or more. However, as will be understood from FIG. 15,such a signal is very small as compared with the whole detected countvalue and includes scattering radiation components. Further, since theincident γ-ray γ₀ is reduced by the collimator 41 e, if the spacialresolution is tried to be raised, the sensitivity fairly deteriorates onthe contrary. FIGS. 16A, 16B, and 16C show examples of distribution percomponent of the radiation which is measured.

FIGS. 16B and 16C show the examples of image information (examples ofthe measured radiation distribution) obtained in the case where twostrong and weak γ-ray sources 16e and 16f exist as shown in FIG. 16A andin the case whose energy levels are different two kinds, γ ray energy ofγ ray sources 16 e, 16 f (140 keV, 511 keV) are observed by the detectorwith the collimator. FIG. 16A shows the positions of the γ-ray sources16 e and 16 f and arrangement of the collimator 41 e and the detectorelements 77. FIG. 16B shows the detection example (example of themeasured radiation distribution) of the γ-ray of 140 keV. FIG. 16C showsthe detection example (example of the measured radiation distribution)of the γ-ray of 511 keV. CdTe is used as a detector element. In bargraphs of FIGS. 16B and 16C, photoelectric absorption (total absorption)of the direct γ-ray, compton scattering of the direct γ-ray, and thescattering radiation of the compton scattered radiation are shown fromthe bottom to the top.

As will be obtained from FIG. 16B, in the γ-ray of 140 keV, since aprobability of the photoelectric effect is higher than that of thecompton scattering, most of the obtained signals are the directradiation γ₀ (ΔE₀₀) and even if the energy discrimination is not made, asufficient clear image can be obtained. However, in the γ-ray of 511 keVof higher energy of FIG. 16C (the γ-ray which is radiated at the time ofthe PET medical examination), most of the γ-ray which is counted is ascattered event or a scattered radiation [γ₀ (ΔE₀₁), γ₁′ (ΔE₁₁′)] .Therefore, if only the γ₀ (ΔE₀₀) component showing the true informationis used, the sensitivity is remarkably lower than that in FIG. 16B, alarge S/N ratio cannot be obtained, and it is difficult to obtain goodpicture quality. To raise the S/N ratio, the detection count number hasto be increased by increasing the imaging time. It is unpreferablebecause a burden on the patient as a subject 17 e increases.

In the second embodiment, the main signal component which is detected ineach detector element 71 a is as shown in FIG. 12. Unlike FIG. 14, thescattering radiation from adjacent pixels γ₁′ is eliminated by theshield 50 b arranged between the detector elements 71 a. Therefore, anenergy spectrum is as shown in FIG. 13. An image which is obtained whenthere is no crosstalk component γ₁′ will be described with reference toFIG. 16 again.

In FIG. 16C showing the measured radiation distribution example of theγ-ray of 511 keV, naturally, it will be understood that the scatteringradiation from adjacent pixels component γ₁′ (ΔE₁₁′) is widelydistributed more than the position of the true γ-ray source and thescattering radiation from adjacent pixels causes the resolution of theimage to deteriorate. Now, assuming that the scattering radiation fromadjacent pixels can be removed by the construction of the embodiment, itwill be understood that the distribution also including the direct γ raycausing compton scattered radiation is not so different from theinformation of 140 keV shown in FIG. 16B. Therefore, as compared withthe prior art in which energy discrimination is carried out to extractγ₀ (ΔE₀₀), in the embodiment in which the compton scattered component inthe detector can be handled as a signal, the fairly high sensitivity(effective count) can be obtained while maintaining the resolution. Thepositional precision is also improved. Naturally, the maintenance iseasy.

As shown in FIG. 6, since the collimator (for example, refer to 41 a inFIG. 2 or the like) does not exist in front of the detector elements 71a, it is considered that the γ-ray enters obliquely. However, theportion of the shield 50 b projecting forwardly more than the detectorelements 71 a plays the same role as the collimator. It is necessary toincrease the thickness (length) of the detector element 71 a for thehigher energy γ-ray and a length of shield 50 b also increases. However,in the case of considering the elongated detector element 71 a as shownin FIG. 6 and the like, since the sensitivity of the detector element 71a itself to the oblique incident component is low, there is particularlyno need to arrange the collimator 41 a as shown in the first embodiment(it will be obviously understood that the construction in which the longcollimator 41 a as shown in FIG. 2 is arranged is not excluded).

In the case of imaging the higher energy γ-ray, the larger effect of theinvention is obtained. Unless the extremely high image resolution isrequested, it is sufficient to set the shield 50 b to a length by whichthe oblique incident component can be suppressed within an allowablerange. A sufficient clear image can be obtained even if the length ofshield 50 b and the length of detector element 71 a are set to an equalvalue so as to obtain an in-plane state as shown in FIG. 8. In FIG. 8,it is also possible to use a construction such that the front edgeportion of the detector element 71 a is projected from a shield 50 e.The improvement of the spacial resolution and the sensitivity by thescattering radiation from adjacent pixels removing effect causes theexamining time to be shortened and provides an effect of remarkablydecreasing a burden on the patient.

Hitherto, a pulse counting system for obtaining the energy and countingis used and the γ-ray is measured while discriminating the energy of theγ-ray. However, according to the system of the construction of thesecond embodiment, it is possible to measure it without needing theenergy discrimination. Therefore, the invention can be also used in acurrent mode of product-sum averaging charge currents generated due tothe extinction of the γ-ray. In the measurement by the current mode,since the energy of the γ-ray is not measured, a construction of themeasuring circuit is simplified. Therefore, also with respect to theASIC for reading, as compared with the case where the ASIC for countingthe pulses can handle only up to tens of channels, the ASIC of one chipcan handle a number of channels such as tens of thousands of channels,the apparatus can be easily designed, and the apparatus can be providedwith lower costs.

Further, by miniaturizing the collimator and reducing its weight oromitting it, a thin size and a light weight of the gamma camera(radiation detector) itself can be realized. For example, in the priorart (refer to FIGS. 26A and 26B), the collimator has a thickness of 60mm, the detector element 77 has a thickness of 15 mm, and the ASICinstalling board 44′ has a thickness of 25 mm, so that a thickness ofabout 100 mm as a whole length is obtained. According to theconstruction (refer to FIG. 6) in the second embodiment, however, if theportion of the shield 50 b projecting from the detector element 71 a issuppressed to 10 mm, it is sufficient to set the total length to about50 mm. Thus, miniaturization of about ½ can be realized and themaintenance consequently becomes easy.

In the conventional gamma camera for high energy, a weight of solecollimator exceeds 100 kg. An example of an external view of acollimator for middle energy is shown for reference in FIG. 27. Forexample, according to a New Medical Apparatus Dictionary of the Societyof Industrial Examination, in the case of a general collimator for lowenergy (about 200 keV), a length is equal to 65 mm, a diameter of holeis equal to 3 mm, and a weight is equal to 54 kg. In the case of ageneral collimator for high energy (>400 keV), a length is equal to 65mm, a diameter of hole is equal to 4 mm, and a weight is equal to 110kg. That is, most of the gamma camera is occupied by the weight ofcollimator. A strength of the apparatus main body (gamma camera casing11, refer to FIG. 1) for supporting the gamma camera is also very largedue to such a weight and an anxiety which is mentally given to thepatient due to a coercive feeling or the like is not small. According tothe construction of the second embodiment, the shield 50 b is equal toabout tens of kg and its weight can be reduced into ⅓. The apparatusitself can be miniaturized. Even in the construction of the gamma cameraof a flexible arm type, a burden on the arm which supports the gammacamera is small and the camera can be easily handled. Since easiness ofhandling of the apparatus is improved as mentioned above, a camerasetting time of the patient can be shortened and the burden on thepatient and the imaging time can be remarkably reduced. The maintenanceis also easy.

As further another embodiment of the second embodiment, as shown in FIG.9, since the number of scattered radiation of low energy compared to γ₀increases as the position of the detector element 71 a approaches therear edge, the shield is divided into a front portion and a rearportion, a material of a high shielding effect is used for a frontshield 51 and a material of a light weight is used for a rear shield 52,so that a weight of the gamma camera itself can be reduced.

According to those embodiments, as shown in FIG. 17, even a gamma cameraobtained by combining a scintillator 31 b and a photodiode 36 can have asimilar construction and a similar effect can be obtained in principleby the shield 50 b. In FIG. 17, reference numeral 42 f denotes adetector module board; 43 f an ASIC module board; 45 f an ASIC; 47 f alight shielding casing; and 48 f and 49 f connectors.

<<Third Embodiment>>

Subsequently, an embodiment regarding the structure of the detectorelements which can be preferably used to the radiation detectors in thefirst and second embodiments will be described with reference to thedrawings (properly refer to FIG. 18A and the like).

The detector element 71 a in FIGS. 18A and 18B, the first embodiment(FIG. 3 and the like), and the second embodiment (FIG. 7 and the like)has a structure such that the pin-shaped anode (anode pin) 72 a isarranged on a center axis, the semiconductor device 74 surrounds aperiphery of the anode 72 a, and a whole side surface of thesemiconductor device 74 is the cathode 73 a. An ordinary detectorelement 171 e as shown in FIGS. 19A and 19B has a structure such thatelectrodes 172 e and 173 e are provided on both surfaces of aplate-shaped semiconductor device 76 called a planer type. To completelycollect the charges generated due to the extinction of the γ-ray in thesemiconductor device 76 of the detector element 171 e, an allowableinterval between the electrodes (interval between the electrodes 172 eand 173 e in FIG. 19A) has an upper limit in dependence on asemiconductor material constructing the semiconductor device. Althoughsuch an interval is determined by mobility and a life of charge carrierand an applied electric field, in the case of the high-energy γ-ray, acertain length of device is needed in the incident direction of theγ-ray as mentioned above. Such a length is longer than the allowableelectrode interval. Therefore, ordinarily, the detector element 171 ehas a construction such that the electrodes 172 e and 173 e are arrangedto two side surfaces in the direction which perpendicularly crosses theincident direction of the γ-ray and the γ-ray is inputted from a gapbetween the electrodes which face each other. To raise the detectingsensitivity, as shown in FIG. 19B, there is also a case where thedetector elements 171 e arranged in parallel are adhered so that thesame electrodes overlap each other and used as one unit detectorelement. The second embodiment in which the shield 50 b (refer to FIG. 6and the like) is arranged around the detector element 71 a has a problemsuch that if such a unit detector element is applied, since the shield50 b has a certain electric potential (cathode potential), the sidesurface portion without the electrode of the detector element 171 e isinfluenced by an electric field due to the electric potential and astrong electric field is locally caused. There is also a problem suchthat an insulating process has to be executed so that the anode 172 eexposed to the side is not come into contact with the shield 50 b towhich the cathode potential is supplied.

The detector element 71 a, which will be explained in the embodiment, isa coaxial element and the whole side surface is the cathode 73 a. Sincethe cathode potential is common, no problem occurs even if the detectorelements 71 a are densely arranged and the adjacent detector elements 71a are come into contact with each other as shown in FIG. 18B. Byallowing the detector elements 71 a to be come into contact with eachother, the same electric potential can be applied to all of the detectorelements 71 a by supplying the current to one position. According tosuch a structure, as shown in FIGS. 11A and 11B, both of the holding ofthe detector elements 71 a and the current supply to them can beexecuted by the cathode spring electrodes 55 a arranged in thelattice-shaped shield 50 b. That is, by applying the cathode potentialto the shield 50 b, the cathode potential is inevitably supplied to allof the detector elements 71 a via the cathodes 73 a. The anodes 72 a aredetection signal terminal and are needed to be independent in eachterminal 71 a. The pin-shaped anode 72 a arranged on the center axiskeeps such independency of each detector element 71 a and enables theelement connection to the detector module board 42 b (refer to FIG. 2and the like) to be made by a simple pin connection. Further, thecoaxial detector element 71 a provides an effect of improving thedetecting efficiency of the γ-ray, which will be explained hereinlater.

As another form of such an element structure, a cathode 75 a and ananode 74 a are evaporation deposited onto each of 4-split detectorelement members 71 b′ as shown in FIG. 20A in consideration ofoperability of the detector element, respectively. Each anode of thefour detector element members 71 b′ is positioned so as to face an anodepin 72 b having a rectangular cross section as shown in FIG. 20B. Onedetector element can be also obtained by the four detector elementmembers 71 b′ by adhering those element members and the anodes 74 a(FIG. 20C).

As shown in FIGS. 21A to 21C, a detector element 71 c can be alsomanufactured by using an anode pin 72 c having a cruciform section. InFIGS. 21A to 21C, reference numeral 71 c′ denotes a detector elementmember; 74 b an anode; and 75 b a cathode.

A phenomenon called a small pixel effect such that by setting an anodearea to be smaller than a cathode area, the energy resolution isimproved. A planer detector element 71 f (FIG. 22B) having oppositeelectrodes called a planer type is constructed in a manner such that anarea of an anode 72 f to collect electrons is set to be smaller thanthat of a cathode 73 f and a plurality of semiconductor device members71 f′ (FIG. 22A) in each of which the anode 72 f and the cathode 73 fare provided on different surfaces are arranged in parallel. Accordingto the detector element 71 f, energy resolution can be further increasedby the small pixel effect. Consequently, the detecting efficiency of theγ-ray is improved.

The increased energy resolution means that the region ΔE₀₀ or ΔE₀₁+ΔE₁₁becomes sharp in FIG. 15. That is, while carrying out energydiscrimination, energy threshold can be increased in FIG. 10, mixingratio of the scattering radiation is decreased, and S/N ratio isimproved. As the result, a more brilliant image can be obtained as sameas the increased sensitivity.

An example of a construction obtained by combining the detector elements71 f and the lattice-shaped shield 50 b is shown in FIG. 10. An exampleof a construction in which the detector elements 71 f are held in theshield 50 b is shown in FIG. 11B. In this case, the detector elements 71f are held in a manner such that the cathode 73 f of the detectorelement 71 f is come into contact with the cathode spring electrodes 55a provided in the shield 50 b. Since the anodes 72 f are not protrudedover the side surface of the detector element, it is not come intocontact with the shield 50 b. Therefore, there is no need to insulatethe shield 50 b and the detector elements 71 f. The contact by thecathode spring electrodes 55 a can be received by the cathodes 73 f onboth sides. Since the anodes 72 f are concentrated on the center portionof the detector element 71 f, an influence of the electric field by thelattice-shaped shield 50 b is small. The above construction can beregarded as a very practical construction from a viewpoint ofmanufacturing of the detector elements 71 f. Owing to such an elementstructure, it is possible to realize a practical gamma camera of theelement separating type using the detector elements in which a pluralityof semiconductor device members are arranged in parallel.

The radiation detector and the detector elements as mentioned above arevery effective in the gamma camera imaging apparatus described withreference to FIG. 1. Besides, it will be naturally understood thatsimilar effects are also obtained by an SPECT (Single Photon EmissionComputed Tomography) apparatus for obtaining a stereoscopic image byrotating two gamma cameras 10 b arranged so as to face each other asshown in FIG. 23. Not only the effect of improvement of the sensitivity(efficient count, increase of S/N ratio) but also advantages common tothose of the gamma camera such as improvement of the maintenanceperformance, reduction of the maintenance costs, realization of the thinshape and light weight of the apparatus, decrease in burden on thepatient owing to the reduction of the examining time, and the like areobtained. Particularly, in the SPECT apparatus using a plurality ofgamma cameras, the improvement of the maintenance performance, thereduction of the maintenance costs, and the realization of the lightweight become large advantages. In the SPECT apparatus, the two gammacameras 10 d (FIG. 6) can be also provided in place of the gamma camera10 b.

In the PET apparatus, there is also a case where the number of imagingpixels is equal to hundreds of thousands of pixels or more. If a largecamera unit is exchanged because there are tens of defective elements,running cost performance fairly increased. Therefore, according to a PETapparatus 25 shown in FIG. 24, a plurality of gamma cameras 10 a eachhaving the detachable detector elements 71 a and the like and theconnector boards (the detector module board 42 a and the ASIC moduleboard 43 a) which can be separated from the ASIC are arranged like aring around the bed 12 a. Thus, the maintenance performance and therunning cost performance of the PET apparatus can be remarkablyimproved. Since the PET apparatus uses the high-energy γ-ray of 511 keVas a target, the detecting efficiency is very low in the prior art asmentioned above. Therefore, the application of the gamma camera 10 a orthe like to the PET apparatus improves the detecting efficiency of theγ-ray and increases the position specifying precision of the detectorelements in which the γ-ray entered. Another gamma camera mentionedabove such as a gamma camera 10 d or the like can be also used in placeof the gamma camera 10 a.

The invention described above are not limited to the foregoingembodiments but many modifications and variations are possible. Forexample, the invention can be embodied by properly combining the firstto third embodiments. Although the embodiments have been describedmainly with respect to the medical application as an example, theapplication is not limited to it but the invention can be widely appliedto general industries, studying application, and the like. Thesemiconductor material of the semiconductor detector elements is notlimited to a specific material either. Although the detector element 71a are detachably held via the spring electrodes 55 a or 55 b, such aholding structure is shown as an example and another holding mechanismcan be also used.

As described above, according to the invention, it is possible tocontribute to the improvement of the detecting efficiency of theradiation in the radiation detector.

It should be further understood by those skilled in the art thatalthough the foregoing description has been made on embodiments of theinvention, the invention is not limited thereto and various changes andmodifications may be made without departing from the spirit of theinvention and the scope of the appended claims.

1. A plurality of radiation detector elements, each comprising: arod-shaped first electrode; a semiconductor device which surrounds anambience of said first electrode and comes into contact with said firstelectrode and into which radiation enters; and a second electrodeprovided for a side surface of said semiconductor device, wherein a partof said first electrode is projected from an edge surface of saidsemiconductor device where said second electrode is not provided; aplurality of radiation detector elements, in which one of said firstelectrode and said second electrode is a signal output electrode foroutputting a radiation detection signal and the other electrode is avoltage applying electrode; an element holding member which detachablyholds said plurality of radiation detector elements and has a pluralityof first electric connecting portions which come into contact with saidsignal output electrode and a plurality of second electric connectingportions which come into contact with said voltage applying electrode;an integrated circuit for processing the radiation detection signaloutputted from said signal output electrode of each of said plurality ofradiation detector elements; and an integrated circuit holding member onwhich said integrated circuit is arranged, wherein said element holdingmember has a plurality of first connector portions separately connectedto said plurality of first electric connecting portions and a secondconnector connected to each of said plurality of second electricconnecting portions, and said integrated circuit holding member has aplurality of third connector portions which are connected to saidintegrated circuit and are separately and detachably attached to saidplurality of first connector portions and a fourth connector portionwhich is detachably attached to said second connector and applies avoltage.
 2. Elements according to claim 1, wherein said second electrodeis provided so as to surround said side surface around saidsemiconductor device and said first electrode, said semiconductor deviceand said second electrode are coaxially arranged.
 3. A detectoraccording to claim 1, wherein a collimator in which a plurality ofradiation paths provided in correspondence to said plurality ofradiation detector elements are formed is arranged on the radiationentering side of said plurality of radiation detector elements.
 4. Adetector according to claim 3, wherein said plurality of radiation pathsare radially arranged in said collimator and said radiation detectorelements are arranged so that a longitudinal direction of said radiationdetector element is located on an extension line of said radiation path.5. A detector according to claim 3, wherein said element holding memberhas a plurality of holding portions to detachably hold said radiationdetector elements and said first electric connecting portion and saidsecond electric connecting portion are provided for each of said holdingportions.
 6. A detector according to claim 5, wherein in said holdingportion, a first hole portion in which a portion including saidsemiconductor device of said radiation detector elements is inserted anda second hole portion in which a projecting portion of the firstelectrode of said radiation detector element is inserted are seriallyarranged, one of said first electric connecting portion and said secondelectric connecting portion is arranged in said first hole portion, andthe other electric connecting portion is arranged in said second holeportion.
 7. A radiation detector comprising: a shield which shieldsradiation and has a plurality of through-holes; a rod-shaped firstelectrode disposed in each of said through holes, a semiconductor devicewhich surrounds an ambience of said first electrode and comes intocontact with said first electrode and into which radiation enters, and asecond electrode provided for a side surface of said semiconductordevice, wherein a part of said first electrode is projected from an edgesurface of said semiconductor device where said second electrode is notprovided; an element holding member to which said radiation detectorelements are detachably attached; wherein a first electric connectingportion which comes into contact with said first electrode is providedfor said element holding member and a second electric connecting portionwhich comes into contact with said second electrode is provided in eachof said through-holes of said shield; an integrated circuit forprocessing a radiation detection signal outputted from said signaloutput electrode of each of said plurality of radiation detectorelements; an integrated circuit holding member on which said integratedcircuit is arranged, wherein said element holding member has a pluralityof first connector portions separately connected to said plurality offirst electric connecting portions and a second connector connected toeach of said plurality of second electric connecting portions, and saidintegrated circuit holding member has a plurality of third connectorportions which are connected to said integrated circuit and areseparately and detachably attached to said plurality of first connectorportions and a fourth connector portion which is detachably attached tosaid second connector and applies a voltage.
 8. A detector according toclaim 7, wherein a length of said shield in an axial direction of saidthrough-hole is equal to or longer than that in said axial direction ofsaid semiconductor device of said radiation detector elements.
 9. Adetector according to claim 7, wherein a length of said shield in anaxial direction of said through-hole is shorter than that in said axialdirection of said semiconductor device of said radiation detectorelements.
 10. A radiation detector element comprising: a plurality ofsemiconductor devices, into which incident radiation enters in a firstdirection, said plurality of semiconductor devices being arranged inparallel to a second direction, said second direction beingperpendicular to said first direction; a first electrode which isarranged between adjacent semiconductor devices of said plurality ofsemiconductor devices, said first electrode comes into contact withfirst side surfaces of said adjacent semiconductor devices, wherein saidfirst electrode is projected from an edge surface of said adjacentsemiconductor devices, said edge surface being located along said firstdirection; a second electrode which comes into contact with second sidesurfaces of said adjacent semiconductor devices, said second sidesurfaces being located along said second direction; a plurality ofradiation detector elements, in which one of said first electrode andsaid second electrode is a signal output electrode for outputting aradiation detection signal and the other electrode is a voltage applyingelectrode; an element holding member which detachably holds saidplurality of radiation detector elements and has a plurality of firstelectric connecting portions which come into contact with said signaloutput electrode and a plurality of second electric connecting portionswhich come into contact with said voltage applying electrode; anintegrated circuit for processing the radiation detection signaloutputted from said signal output electrode of each of said plurality ofradiation detector elements; and an integrated circuit holding member onwhich said integrated circuit is arranged, wherein said element holdingmember has a plurality of first connector portions separately connectedto said plurality of first electric connecting portions and a secondconnector connected to each of said plurality of second electricconnecting portions, and said integrated circuit holding member has aplurality of third connector portions which are connected to saidintegrated circuit and are separately and detachably attached to saidplurality if first connector portions and a fourth connector portionwhich is detachably attached to said second connector and applies avoltage.
 11. An element according to claim 10, wherein a width of saidfirst electrode is narrower than that of said second electrode.
 12. Adetector according to claim 10, wherein a collimator, in which aplurality of radiation paths provided in correspondence to saidplurality of radiation detector elements are formed, is arranged on aradiation entering side of said plurality of radiation detectorelements.
 13. A detector according to claim 12, wherein said pluralityof radiation paths are radially arranged in said collimator and saidradiation detector elements are arranged so that a longitudinaldirection of said radiation detector element is located on an extensionline of said radiation paths.
 14. A detector according to claim 12,wherein said element holding member has a plurality of holding portionsto detachably hold said radiation detector elements and said firstelectric connecting portions and said second electric connectingportions are provided for each of said holding portions.
 15. A detectoraccording to claim 14, wherein in said plurality of holding portions, afirst hole portion in which a portion including said semiconductordevice of said radiation detector elements is inserted and a second holeportion in which a projecting portion of the first electrode of saidradiation detector element is inserted are serially arranged, one ofsaid first electric connecting portion and said second electricconnecting portion is arranged in said first hole portion, and the otherelectric connecting portion is arranged in said second hole portion. 16.A radiation detector comprising: a shield which shields incidentradiation and has a plurality of through-holes; radiation detectorelements arranged in each of said through-holes; a plurality ofsemiconductor devices into which said incident radiation enters along afirst direction, said plurality of semiconductor devices being arrangedin parallel with a second direction which is perpendicular to said firstdirection; a first electrode which is arranged between adjacentsemiconductor devices of said plurality of semiconductor devices,wherein said first electrode comes into contact with side surfaces ofsaid adjacent semiconductor devices; and a second electrode which comesinto contact with second side surfaces of said adjacent semiconductordevices, said second side surfaces being located along said seconddirection, wherein said first electrode is projected from one edgesurface located along said first direction of said adjacentsemiconductor devices, and wherein a width of said first electrode isnarrower than a width of said second electrode; an element holdingmember which detachably holds said radiation detector elements; aplurality of first electric connecting portions which come into contactwith a signal output electrode disposed at said element holding member,and a plurality of second electric connecting portions which come intocontact with a voltage applying electrode in each of said through-holesof said shield; an integrated circuit for processing a radiationdetection signal outputted from said signal output electrode of each ofsaid plurality of radiation detector elements; an integrated circuitholding member on which said integrated circuit is arranged, whereinsaid element holding member has a plurality of first connector portionsseparately connected to said plurality of first electric connectingportions and a second connector connected to each of said plurality ofsecond electric connecting portions, and wherein said integrated circuitholding member has a plurality of third connector portions which areconnected to said integrated circuit and are separately and detachablyattached to said plurality of first connector portions and a fourthconnector portion which is detachably attached to said second connectorand applies a voltage.
 17. A detector according to claim 16, wherein alength of said shield in an axial direction of said through-hole isequal to or longer than that in an axial direction of said semiconductordevice of said radiation detector elements.
 18. A detector according toclaim 16, wherein a length of said shield in an axial direction of saidthrough-hole is shorter than that in an axial direction of saidsemiconductor device of said radiation detector elements.